Pneumatic tube conveyors are in common use in stores, hospitals, office buildings and the like for use in carrying messages, supplies etc. between various points in the building. Such systems operate by generating a pressure differential between two points, either by pressurizing at the sending point or applying a vacuum at the receiving point. The carriers each have at least one seal ring around it so that they function in the nature of a piston to be projected through the tube. Because the carrier fits fairly snugly within the tube changes in direction require bends of extremely large radius which often require that curved section of tubing extend into space which could be utilized otherwise. On certain descending runs, curves of lesser radius are possible by enlarging the cross section of the dimension radially of the curve so that the carrier has more room to turn sharply. In such case, the carrier is projected to the curve by pressure differential and then allowed to fall around the curve by gravity. However, short radius curves of increased cross section have not been possible for upward carrier movements since, when the section of enlarged dimension is reached, pressure differential is lost around the carrier and the propelling force is lost.